diff --git a/capa/engine.py b/capa/engine.py
index ee103866..649d0367 100644
--- a/capa/engine.py
+++ b/capa/engine.py
@@ -102,14 +102,14 @@ class And(Statement):
         super().__init__(description=description)
         self.children = children
 
-    def evaluate(self, ctx, short_circuit=True):
+    def evaluate(self, features: FeatureSet, short_circuit=True):
         capa.perf.counters["evaluate.feature"] += 1
         capa.perf.counters["evaluate.feature.and"] += 1
 
         if short_circuit:
             results = []
             for child in self.children:
-                result = child.evaluate(ctx, short_circuit=short_circuit)
+                result = child.evaluate(features, short_circuit=short_circuit)
                 results.append(result)
                 if not result:
                     # short circuit
@@ -117,7 +117,7 @@ class And(Statement):
 
             return Result(True, self, results)
         else:
-            results = [child.evaluate(ctx, short_circuit=short_circuit) for child in self.children]
+            results = [child.evaluate(features, short_circuit=short_circuit) for child in self.children]
             success = all(results)
             return Result(success, self, results)
 
@@ -135,14 +135,14 @@ class Or(Statement):
         super().__init__(description=description)
         self.children = children
 
-    def evaluate(self, ctx, short_circuit=True):
+    def evaluate(self, features: FeatureSet, short_circuit=True):
         capa.perf.counters["evaluate.feature"] += 1
         capa.perf.counters["evaluate.feature.or"] += 1
 
         if short_circuit:
             results = []
             for child in self.children:
-                result = child.evaluate(ctx, short_circuit=short_circuit)
+                result = child.evaluate(features, short_circuit=short_circuit)
                 results.append(result)
                 if result:
                     # short circuit as soon as we hit one match
@@ -150,7 +150,7 @@ class Or(Statement):
 
             return Result(False, self, results)
         else:
-            results = [child.evaluate(ctx, short_circuit=short_circuit) for child in self.children]
+            results = [child.evaluate(features, short_circuit=short_circuit) for child in self.children]
             success = any(results)
             return Result(success, self, results)
 
@@ -162,11 +162,11 @@ class Not(Statement):
         super().__init__(description=description)
         self.child = child
 
-    def evaluate(self, ctx, short_circuit=True):
+    def evaluate(self, features: FeatureSet, short_circuit=True):
         capa.perf.counters["evaluate.feature"] += 1
         capa.perf.counters["evaluate.feature.not"] += 1
 
-        results = [self.child.evaluate(ctx, short_circuit=short_circuit)]
+        results = [self.child.evaluate(features, short_circuit=short_circuit)]
         success = not results[0]
         return Result(success, self, results)
 
@@ -185,7 +185,7 @@ class Some(Statement):
         self.count = count
         self.children = children
 
-    def evaluate(self, ctx, short_circuit=True):
+    def evaluate(self, features: FeatureSet, short_circuit=True):
         capa.perf.counters["evaluate.feature"] += 1
         capa.perf.counters["evaluate.feature.some"] += 1
 
@@ -193,7 +193,7 @@ class Some(Statement):
             results = []
             satisfied_children_count = 0
             for child in self.children:
-                result = child.evaluate(ctx, short_circuit=short_circuit)
+                result = child.evaluate(features, short_circuit=short_circuit)
                 results.append(result)
                 if result:
                     satisfied_children_count += 1
@@ -204,7 +204,7 @@ class Some(Statement):
 
             return Result(False, self, results)
         else:
-            results = [child.evaluate(ctx, short_circuit=short_circuit) for child in self.children]
+            results = [child.evaluate(features, short_circuit=short_circuit) for child in self.children]
             # note that here we cast the child result as a bool
             # because we've overridden `__bool__` above.
             #
@@ -214,7 +214,7 @@ class Some(Statement):
 
 
 class Range(Statement):
-    """match if the child is contained in the ctx set with a count in the given range."""
+    """match if the child is contained in the feature set with a count in the given range."""
 
     def __init__(self, child, min=None, max=None, description=None):
         super().__init__(description=description)
@@ -222,15 +222,15 @@ class Range(Statement):
         self.min = min if min is not None else 0
         self.max = max if max is not None else (1 << 64 - 1)
 
-    def evaluate(self, ctx, **kwargs):
+    def evaluate(self, features: FeatureSet, short_circuit=True):
         capa.perf.counters["evaluate.feature"] += 1
         capa.perf.counters["evaluate.feature.range"] += 1
 
-        count = len(ctx.get(self.child, []))
+        count = len(features.get(self.child, []))
         if self.min == 0 and count == 0:
             return Result(True, self, [])
 
-        return Result(self.min <= count <= self.max, self, [], locations=ctx.get(self.child))
+        return Result(self.min <= count <= self.max, self, [], locations=features.get(self.child))
 
     def __str__(self):
         if self.max == (1 << 64 - 1):
@@ -250,7 +250,7 @@ class Subscope(Statement):
         self.scope = scope
         self.child = child
 
-    def evaluate(self, ctx, **kwargs):
+    def evaluate(self, features: FeatureSet, short_circuit=True):
         raise ValueError("cannot evaluate a subscope directly!")
 
 
diff --git a/capa/features/common.py b/capa/features/common.py
index 5cbe684d..4b02b5ce 100644
--- a/capa/features/common.py
+++ b/capa/features/common.py
@@ -166,10 +166,10 @@ class Feature(abc.ABC):  # noqa: B024
     def __repr__(self):
         return str(self)
 
-    def evaluate(self, ctx: Dict["Feature", Set[Address]], **kwargs) -> Result:
+    def evaluate(self, features: "capa.engine.FeatureSet", short_circuit=True) -> Result:
         capa.perf.counters["evaluate.feature"] += 1
         capa.perf.counters["evaluate.feature." + self.name] += 1
-        return Result(self in ctx, self, [], locations=ctx.get(self, set()))
+        return Result(self in features, self, [], locations=features.get(self, set()))
 
 
 class MatchedRule(Feature):
@@ -207,7 +207,7 @@ class Substring(String):
         super().__init__(value, description=description)
         self.value = value
 
-    def evaluate(self, ctx, short_circuit=True):
+    def evaluate(self, features: "capa.engine.FeatureSet", short_circuit=True):
         capa.perf.counters["evaluate.feature"] += 1
         capa.perf.counters["evaluate.feature.substring"] += 1
 
@@ -216,7 +216,7 @@ class Substring(String):
         matches: typing.DefaultDict[str, Set[Address]] = collections.defaultdict(set)
 
         assert isinstance(self.value, str)
-        for feature, locations in ctx.items():
+        for feature, locations in features.items():
             if not isinstance(feature, (String,)):
                 continue
 
@@ -299,7 +299,7 @@ class Regex(String):
                 f"invalid regular expression: {value} it should use Python syntax, try it at https://pythex.org"
             ) from exc
 
-    def evaluate(self, ctx, short_circuit=True):
+    def evaluate(self, features: "capa.engine.FeatureSet", short_circuit=True):
         capa.perf.counters["evaluate.feature"] += 1
         capa.perf.counters["evaluate.feature.regex"] += 1
 
@@ -307,7 +307,7 @@ class Regex(String):
         # will unique the locations later on.
         matches: typing.DefaultDict[str, Set[Address]] = collections.defaultdict(set)
 
-        for feature, locations in ctx.items():
+        for feature, locations in features.items():
             if not isinstance(feature, (String,)):
                 continue
 
@@ -384,12 +384,12 @@ class Bytes(Feature):
         super().__init__(value, description=description)
         self.value = value
 
-    def evaluate(self, ctx, **kwargs):
+    def evaluate(self, features: "capa.engine.FeatureSet", short_circuit=True):
         capa.perf.counters["evaluate.feature"] += 1
         capa.perf.counters["evaluate.feature.bytes"] += 1
 
         assert isinstance(self.value, bytes)
-        for feature, locations in ctx.items():
+        for feature, locations in features.items():
             if not isinstance(feature, (Bytes,)):
                 continue
 
@@ -434,11 +434,11 @@ class OS(Feature):
         super().__init__(value, description=description)
         self.name = "os"
 
-    def evaluate(self, ctx, **kwargs):
+    def evaluate(self, features: "capa.engine.FeatureSet", short_circuit=True):
         capa.perf.counters["evaluate.feature"] += 1
         capa.perf.counters["evaluate.feature." + self.name] += 1
 
-        for feature, locations in ctx.items():
+        for feature, locations in features.items():
             if not isinstance(feature, (OS,)):
                 continue
 
diff --git a/tests/test_engine.py b/tests/test_engine.py
index 785896a3..c942ed67 100644
--- a/tests/test_engine.py
+++ b/tests/test_engine.py
@@ -93,10 +93,10 @@ def test_complex():
 def test_range():
     # unbounded range, but no matching feature
     # since the lower bound is zero, and there are zero matches, ok
-    assert bool(Range(Number(1)).evaluate({Number(2): {}})) is True
+    assert bool(Range(Number(1)).evaluate({Number(2): {}})) is True  # type: ignore
 
     # unbounded range with matching feature should always match
-    assert bool(Range(Number(1)).evaluate({Number(1): {}})) is True
+    assert bool(Range(Number(1)).evaluate({Number(1): {}})) is True  # type: ignore
     assert bool(Range(Number(1)).evaluate({Number(1): {ADDR1}})) is True
 
     # unbounded max
@@ -112,12 +112,12 @@ def test_range():
     assert bool(Range(Number(1), max=2).evaluate({Number(1): {ADDR1, ADDR2, ADDR3}})) is False
 
     # we can do an exact match by setting min==max
-    assert bool(Range(Number(1), min=1, max=1).evaluate({Number(1): {}})) is False
+    assert bool(Range(Number(1), min=1, max=1).evaluate({Number(1): {}})) is False  # type: ignore
     assert bool(Range(Number(1), min=1, max=1).evaluate({Number(1): {ADDR1}})) is True
     assert bool(Range(Number(1), min=1, max=1).evaluate({Number(1): {ADDR1, ADDR2}})) is False
 
     # bounded range
-    assert bool(Range(Number(1), min=1, max=3).evaluate({Number(1): {}})) is False
+    assert bool(Range(Number(1), min=1, max=3).evaluate({Number(1): {}})) is False  # type: ignore
     assert bool(Range(Number(1), min=1, max=3).evaluate({Number(1): {ADDR1}})) is True
     assert bool(Range(Number(1), min=1, max=3).evaluate({Number(1): {ADDR1, ADDR2}})) is True
     assert bool(Range(Number(1), min=1, max=3).evaluate({Number(1): {ADDR1, ADDR2, ADDR3}})) is True